The past three weeks have brought us many cloudy days and some rain. This has been a blessing because it has helped relieve some of our plants from drought conditions, and it has helped reduce the number of chinch bugs that were attacking lawns with St. Augustine grass.
The cloudy weather and cooler temperatures bring some disease problems to lawns. The major disease that is starting to occur is large patch. Large patch is caused by the fungus Rhizoctonia.
Large patch is a disease that occurs in the spring and fall. It likes to grow when the daytime temperature is higher than 80 degrees, and the nighttime temperature is higher than 55 degrees.
So, why is large patch such a problem in the spring and fall? This is the time of the year when turf grasses are coming out of or going into dormancy. The grasses are not growing as actively as during other times of the year and are more stressed. Plants that are stressed are more likely to get a disease.
Rhizoctonia grows best when it has a good supply of nitrogen. This is why fertilizing too early in the spring or winterizing your grass can increase the chance of large patch. Applying high levels of potassium can improve turf's disease resistance. Potassium is the last number on the fertilizer bag, and it helps the plant by increasing disease resistance, drought resistance and winter hardiness. Use a fertilizer that has more potassium in it for the first application in the spring and the last application in late summer. A good fertilizer analysis to use is 16-4-8.
Another factor that can increase the chance of large patch is improper irrigation. Not only does Rhizoctonia like cooler temperatures and high nitrogen levels, but it likes excessive moisture levels as well. As the temperature starts to cool off, reduce the amount of water applied to your lawn, water deeper and less often. This allows the grass to dry between irrigations, thus reducing the chance of large patch.
Proper watering and fertilization are the first steps to treating large patch. The next step is to treat with a fungicide. There are numerous fungicides on the market that will work on large patch. In order for them to work properly, you must follow the directions on the label. Most of these products will need a second application for them to work.
The fungicides that work well on large patch are thiophanate methyl, triadimefon, myclobutanil, maneb, mancozeb, PCNB, and captan. These products can be purchased by home-owners and most of them can be found at garden centers.
Another problem in the fall is rust. Rust is caused by the fungus Puccinia sp, and the main grass it affects in our area is zoysia. This disease also attacks plants that are slowing down their growth and starting to go dormant, and will cause orange-colored lesions to appear on the leaves. You can wipe the spores off with your finger and your finger will be orange. Rust will seldom kill the grass, but it does weaken it going into the winter. You can see some thinning of the turf the next spring.
To help reduce the chance of rust, follow the same management practices for reducing large patch. To control both large patch and rust, it helps to control the thatch layer in turf. Thatch is made up of stems, stolons, and other woody parts of the grass plant that builds up on the soil surface. It is not made up of grass leaves.
Thatch less than a half-inch thick doesn't cause problems, but it needs to be managed once it gets deeper. Thatch is the home for fungi. This is where they live and work. Thatch will inhibit pesticides, fertilizers and water from reaching the soil surface. Reducing thatch reduces the chance of disease and helps solve disease problems.
You can control rust problems with the same fungicides that you used to control large patch. However, the best way to control these diseases is to manage turf properly.
Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at email@example.com. The Extension Web address is www.ugaextension.com/columbia.
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